1. Technical Field
The present invention relates to a technique for performing gray-scale display control by a sub-field driving method.
2. Related Art
As gray-scale controlling methods in liquid crystal elements, a so-called sub-field driving method in which a time for applying a constant voltage to a liquid crystal element is modulated, in addition to a voltage modulation method in which a voltage to be applied to a liquid crystal element is modulated, has been known (JP-A-2003-114661). In the sub-field driving method, one frame is divided into a plurality of sub-fields. The gray scale of a liquid crystal element is controlled by a combination of a sub-field in which voltage application is ON and a sub-field in which voltage application is OFF in the plurality of sub-fields. Moreover, in the liquid crystal element, a driving of temporally switching the polarity of an applied voltage is performed for preventing the image sticking or degradation of liquid crystal. Ideally, it is desirable that after performing writing with a positive voltage, writing with a negative voltage is performed for the same time. Therefore, one frame is divided into halves, and gray-scale control is performed using sub-fields included in the half of the frame.
In recent years, techniques for performing 3D display (stereoscopic display) have been developed. JP-A-9-138384 discloses a technique for time-divisionally displaying a left-eye image and a right-eye image. A user visually recognizes the video through glasses with shutters. The shutter of a right-eye portion of the glasses is closed when the left-eye image is displayed, while the shutter of a left-eye portion of the glasses is closed when the right-eye image is displayed. With the use of the device, different images are visually recognized respectively with the left eye and the right eye, so that 3D display is perceived.
For example, when a sub-field driving method is adopted as a gray-scale controlling method in performing 3D display using the glasses described above, the number of sub-fields capable of being used for the gray-scale control is reduced to half compared to the case of 2D display. The number of gray scales capable of being expressed in the sub-field driving correlates with the number of sub-fields, so that a reduction in the number of sub-fields means a reduction in the number of gray scales capable of being expressed. This is not a problem which is limited to the case of performing 3D display, but is an essential problem of the sub-field driving method in which a limited time as one frame is divided into a finite number of sub-fields for driving.